Device and method for separating components of a fluid sample

ABSTRACT

A device and method is provided for separating heavier and lighter fractions of a fluid sample. The device includes a plurality of constituents comprising a container and a composite element in the container. The composite element is a separator comprising at least two components and more particularly an elastic portion and a plug member. A fluid sample is delivered to the container and the device is subjected to centrifugation whereby the centrifugal load causes the elastic portion of the separator to deform so that the separator migrates into the fluid sample and stabilizes between the heavier and lighter fractions of the fluid sample. The elastic portion of the separator will resiliently return to its initial configuration upon termination of the centrifugal load such that the elastic portion sealingly engages the container and separates the heavier and lighter fractions of the fluid sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/142,787, filed May 13, 2002, which claims priority to U.S. patentapplication Ser. No. 09/454,268 filed Dec. 3, 1999, which claimspriority to U.S. Pat. App. Ser. No. 60/110,937, filed Dec. 5, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device and method for separating heavier andlighter fractions of a fluid sample. More particularly, this inventionrelates to a device and method for collecting and transporting fluidsamples whereby the device and fluid sample are subjected tocentrifugation to cause separation of the heavier fraction from thelighter fraction of the fluid sample.

2. Description of Related Art

Diagnostic tests may require separation of a patient's whole bloodsample into components, such as serum or plasma, the lighter phasecomponent, and red blood cells, the heavier phase component. Samples ofwhole blood are typically collected by venipuncture through a cannula orneedle attached to a syringe or an evacuated collection tube. Separationof the blood into serum or plasma and red blood cells is thenaccomplished by rotation of the syringe or tube in a centrifuge. Sucharrangements use a barrier for moving into an area adjacent the twophases of the sample being separated to maintain the componentsseparated for subsequent examination of the individual components.

A variety of devices have been used in collection devices to divide thearea between the heavier and lighter phases of a fluid sample.

The most widely used device includes thixotropic gel materials such aspolyester gels in a tube. The present polyester gel serum separationtubes require special manufacturing equipment to prepare the gel and tofill the tubes. Moreover, the shelf-life of the product is limited inthat over time globules may be released from the gel mass. Theseglobules have a specific gravity that is less than the separated serumand may float in the serum and may clog the measuring instruments, suchas the instrument probes used during the clinical examination of thesample collected in the tube. Such clogging can lead to considerabledowntime for the instrument to remove the clog.

No commercially available gel is completely chemically inert to allanalytes. If certain drugs are present in the blood sample when it istaken, there can be an adverse chemical interaction with the gelinterface.

Therefore, a need exists for a separator device that (i) is easily usedto separate a blood sample; (ii) is independent of temperature duringstorage and shipping; (iii) is stable to radiation sterilization; (iv)employs the benefits of a thixotropic gel barrier yet avoids the manydisadvantages of placing a gel in contact with the separated bloodcomponents; (v) minimizes cross contamination of the heavier and lighterphases of the sample during centrifugation; (vi) minimizes adhesion ofthe lower and higher density materials against the separator device;(vii) can be used with standard sampling equipment; (viii) is able tomove into position to form a barrier in less time than conventionalmethods and devices; and (ix) is able to provide a clearer specimen withless cell contamination than conventional methods and devices.

SUMMARY OF THE INVENTION

The present invention is a method and assembly for separating a fluidsample into a higher specific gravity phase and a lower specific gravityphase. Desirably, the assembly of the present invention comprises aplurality of constituents. Preferably, the assembly comprises acontainer and a composite element.

Most preferably, the container is a tube and the composite element is aseparator arranged to move in the tube under the action of centrifugalforce in order to separate the portions of a fluid sample. Preferably,the separator is a radically deformable seal plug.

Most preferably, the separator is used within a container such as atube. The tube comprises an open end, a closed end and a sidewallextending between the open end and closed end. The sidewall comprises anouter surface and an inner surface. The tube further comprises a closuredisposed to fit in the open end of the tube with a resealable septum.Preferably, the separator element is releaseably positioned at the openend of the tube with the bottom area of the closure.

Most preferably, the separator consists of two components. Preferably,the composite element comprises an overall specific gravity at a targetspecific gravity of σ_(t). The target specific gravity is that requiredto separate a fluid sample into at least two phases. Preferably, theseparator comprises at least two or more regions of differing specificgravities. Preferably, at least one of the regions is higher than thetarget specific gravity and at least one of the regions is lower thanthe target specific gravity.

Desirably, the separator comprises a low density plastic body and a highdensity elastomeric seal diaphragm. The separator as a whole is sized tofit releasably within the tube with an interference fit against theinner surface of the sidewall of the-tube.

Preferably, the plastic body has a hollow core or a central passage anda hollow chamber surrounding the hollow core. The plastic body has aspecific gravity of about 1.1 to about 7.9.

Desirably, the plastic body is a substantially rigid moldablethermoplastic material such as polystyrene, polyethylene, polypropylene,and mixtures thereof that is inert to the fluid sample of interest.

Desirably, the elastomeric seal diaphragm comprises a fill septum tofacilitate needle penetration during the blood fill cycle and an annularskirt that is able to deform during the centrifugation process andreduce the overall diameter of the separator.

Desirably, the plastic body is nested within the elastomeric sealdiaphragm, whereby the channel of the plastic body is in directcommunication with the fill septum of the elastomeric seal diaphragm.

Desirably, the elastomeric seal diaphragm may be comprised of anynatural or synthetic elastomer or mixture thereof, that is inert to thefluid sample of interest. Preferably, the elastomeric seal diaphragm ismade from an elastomer having a 50% tensile modulus from about 0.1 MPato about 1.4 MPa.

Preferably, the separator has a density of about 1.028 to about 1.09g/cc so that the separator will come to rest after centrifugal force, atsubstantially at the border between the heavier and lighter phases ofthe fluid sample under consideration, and most preferably between theheavier and lighter phases of a blood sample. Preferably, the separatorwill function under load created by an applied acceleration of about 300g to about 3000 g.

Preferably, the separator is initially secured to the bottom area of theclosure. Desirably, the bottom area of the closure includes anintegrally molded gripping means for releasably holding the elastomericseal diaphragm of the separator with the closure until the assembly issubjected to centrifugation at which time the separator is released fromthe gripping means of the closure. The separator is further fitted withthe tube whereby the annular skirt of the elastomeric seal diaphragm,which provides the largest diameter of the separator in its undeformedstate, has an interference fit with the inner surface of the sidewall ofthe tube.

In use, a fluid sample enters the assembly by needle. The needlepenetrates the closure and the elastomeric seal diaphragm of theseparator. The sample enters the assembly through the needle and throughthe channel of the plastic body and into the body of the tube. Theneedle is withdrawn from the assembly and the septum of the closure andthe elastomeric seal diaphragm reseal.

The assembly is then subjected to centrifugation. Under centrifugation,the separator is released from the closure. The separator migratesaxially down the tube towards the closed end. The migration isfacilitated by the density of the plastic body versus the density of theelastomeric seal diaphragm of the separator. The annular skirt of theelastomeric seal diaphragm temporarily deforms under centrifugation,whereby the diameter is reduced eliminating its interference fit withthe inner wall surface of the tube. Therefore, a path is developedbetween the inner wall of the tube and the separator that permits theflow of the low density component past the separator as it migrates downthe tube. Migration of the separator terminates when it reaches theposition between the lower density liquid component and higher densitycellular/solid components, equal to its overall density. Uponterminating centrifugation, the annular skirt of the elastomeric sealdiaphragm returns to its undeformed shape, sealing against the innerwall of the tube, thereby creating a barrier between the higher andlower density components of the fluid.

The separator's position at the top of the tube in conjunction with theclosure and the elastomeric seal diaphragm's penetrable area into thepassage throughway of the separator, provides easy direct loading of thefluid sample into the tube without any obstructions. Thus, the fluidsample is easily delivered into the tube without exposing theuncentrifuged fluid sample to the outer surface area of the separator.

However, it is within the purview of the invention that the separatormay be placed at the bottom of the tube as well.

Thus, when the container is subjected to centrifugation, the separatormoves away from the grip of the closure and towards a position betweenthe lower and higher specific gravity phases of the fluid sample.

When the fluid sample is blood, the higher specific gravity portion thatcontains the cellular components is between the separator and the bottomof the container after centrifugation. The lower specific gravityportion that contains the cell free serum fraction or plasma is betweenthe top surface of the separator and the top of the container aftercentrifugation.

Therefore, at the final position of the separator after centrifugation,the separator is able to substantially eliminate the presence of redblood cells in the lower specific gravity portion and the lower specificgravity portion is substantially free of cellular contamination.

The assembly of the present invention is advantageous over existingseparation products that use gel. In particular the assembly of thepresent invention will not interfere with analytes as compared to gelsthat may interfere with certain analytes. Another attribute of thepresent invention is that the assembly of the present invention will notinterfere with therapeutic drug monitoring analytes.

Most notably, the time to separate a fluid sample into separatedensities is achieved in substantially less time with the assembly ofthe present invention as compared to assemblies that use gel.

Another notable advantage of the present invention is that fluidspecimens are not subjected to low density gel residuals that are attimes available in products that use gel.

A further attribute of the present invention is that there is nointerference with instrument probes.

Another attribute of the present invention is that samples for bloodbanking tests are more acceptable than when a gel separator is used.

Another attribute of the present invention is that only thesubstantially cell-free serum fraction of a blood sample is exposed tothe top surface of the separator, thus providing practitioners with aclean sample.

Additionally, the assembly of the present invention does not require anyadditional steps or treatment by a medical practitioner, whereby a bloodor fluid sample is drawn in the standard fashion, using standardsampling equipment.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the assembly of the present invention.

FIG. 2 is a longitudinal sectional view of the assembly of FIG. 1 takenalong line 2-2 thereof.

FIG. 3 is a longitudinal sectional view of the assembly of FIG. 1 takenalong line 2-2 thereof illustrating fluid delivery into the assembly bya needle.

FIG. 4 illustrates the assembly under centrifugation and the release ofthe separator from the gripping means of the closure.

FIG. 5 illustrates the assembly after certrifugation and the separationof the liquid sample into higher and lower specific gravities.

FIG. 6 is a perspective view of the separator of the present invention.

FIG. 7 is a longitudinal sectional view of the separator of FIG. 6 takenalong line 7-7 thereof.

DETAILED DESCRIPTION

The present invention may be embodied in other specific forms and is notlimited to any specific embodiments described in detail, which aremerely exemplary. Various other modifications will be apparent to andreadily made by those skilled in the art without departing from thescope and spirit of the invention. The scope of the invention will bemeasured by the appended claims and their equivalents.

The preferred apparatus of the present invention is illustrated in FIGS.1 to 5, wherein assembly 20 comprises a tube 30, a closure 50 and aseparator 70.

Tube 30 has an open end 32 that includes a top edge 33, a closed end 34and a sidewall 36 extending between the open end and the closed end.Sidewall 36 has an outer surface 38 and an inner surface 40. Tube 30defines a receptacle with a central axis “A”.

Tube 30 is preferably made from a substantially transparent and rigidmaterial. Suitable materials for the tube include glass, polystyrene,polyethyleneterephthalate, polycarbonate and the like.

Closure 50 is disposed to fit over open end 32 of tube 30. Closure 50comprises an annular upper portion 52 which extends over top edge 33 ofsidewall 36 and a lower annular portion or skirt 54 of lesser diameterthan the annular upper portion 52 which extends into and forms aninterference fit with inner surface 40 of sidewall 36 for maintainingstopper 50 in place in open end 32.

Annular upper portion 52 includes a top surface area 56, sidewall 58that converges from surface area 56 towards upper well area 60. Wellarea 60 is most preferably a thin diaphragm or a self sealing septum fordirecting and receiving the point of a needle to be inserted into andthrough the stopper. The self sealing septum material allows penetrationby a piercing element such as a needle and then reseals when thepiercing element is withdrawn.

An annular ledge or abutment 57 separates annular upper portion 52 andlower annular portion 54. Located on bottom surface 68 of lower annularportion 54 are gripping means 69 that are used to initially align andhold the separator in the assembly.

Preferably, the closure may be made of natural rubber elastomer,synthetic thermoplastic and thermoset elastomeric materials. Preferably,the closure is made of a resilient elastomeric material whereby theseptum is self-sealing.

As shown in FIGS. 6 and 7, separator 70 is a dual separator assemblyincluding a molded seal body 90 and an elastomeric hat shaped flexibleseal diaphragm 72. Flexible seal diaphragm 72 includes a top surface 73,an annular skirt 74 extending downwardly from the top surface to ajunction 76 and a flanged annular skirt 78 extending outwardly anddownwardly from the junction to a stop surface 79 with a rounded end 80.Top surface 73 is most preferably a self sealing septum.

Seal body 90 includes a top surface 86, a bottom surface 88, an annularupper portion 90 extending from the top surface to an indented junction91, a flanged outer sidewall 92 extending downwardly and outwardly andtapers towards a junction 93, and a second outer sidewall 96 extendingfrom junction 93 downwardly to bottom surface 88. Inside of seal body 84is a passageway 98 and a cavity 100. Passageway 98 extends from topsurface 86 to bottom surface 88. Passageway 98 mates with top surface 73of annular skirt 74 of flexible seal diaphragm 72 whereby when apiercing element goes through top surface 73 it will extend directlyinto passageway 98 without any interference.

As shown in FIG. 7, annular upper portion 90 of seal body 84 is nestedin annular skirt 74 of flexible seal diaphragm 72. Friction fit, anadhesive or the like may be used to maintain the nesting of the twocomponents. The separator is then held at the top end of the tube bygripping means 69 of the closure. As shown in FIG. 2, rounded end 80 offlexible seal diaphragm 72 and the inner wall of the tube form aninterference fit. The seal body does not interfere with the inner wallof the tube as shown in FIG. 2, because the diameter of flanged annularskirt 78 of flexible seal diaphragm 72 is larger than the diameter ofseal body 90.

As shown in FIG. 3, a fluid sample A is delivered to the tube by aneedle that penetrates closure 50 in upper well area 60 and then topsurface 73 of flexible seal diaphragm 72. For purposes of illustrationonly, the fluid sample is blood. The fluid sample is delivered into theaxial passageway of the separator so that the fluid sample is introducedbetween closed end 34 of the tube and the separator whereby the outersurface of all components of the separator are substantially free of anycontact with the fluid sample.

As shown in FIG. 4 when assembly 20 is subjected to centrifugation oraxial centrifugation force, separator 70 releases from gripping means 69of closure 50 and descends towards closed end 34 of tube 30. As theseparator descends, a lower specific gravity fraction B of fluid sampleA moves upwardly past the separator.

As shown in FIG. 4 as the separator descends, flanged annular skirt 78of the elastomeric seal deforms, reducing its diameter and eliminatingits interference with the inner wall of the tube. This opens up a path100 between the tube and the separator, permitting the flow of the fluidpast the separator as the separator migrates down the tube. The residuallow density component inside passageway 98 of the separator will migratedownwardly and upwardly past the separator.

As illustrated in FIG. 5, after centrifugation is complete,centrifugation is terminated, the elastomeric seal diaphragm returns toits undeformed shape, sealing against the inner wall of the tube,whereby separator 70 serves as a divider between lower specific gravityportion B and higher specific gravity portion C of the fluid sample.

Tube 30 is compatible with most of the numerous additives used in samplecollection tubes such as citrates, silicates, EDTA and the like that areused to condition the sample either to facilitate or retard clotting, orto preserve the sample for a particular analysis. It is within thepurview of this invention that one or more additives may be used in thepresent invention for particular applications.

1. An assembly for separating a fluid sample into a higher specificgravity phase and a lower specific gravity phase comprising: an elongatesample tube having an open end, a closed end and a cylindrical tube walltherebetween; a closure positionable over said open end of said tube; aseparator element comprising a plastic body and an elastomeric sealdiaphragm in said tube; said plastic body comprising a hollow core; saidelastomeric seal diaphragm comprising a septum and an annular skirt; andsaid plastic body is nested with said elastomeric seal diaphragm wherebysaid hollow core of said plastic body is in communication with saidseptum of said elastomeric seal diaphragm.
 2. The assembly of claim 1,wherein the separator assembly is adjacent to the closure.
 3. Theassembly of claim 1, wherein the separator assembly is coupled to theclosure.
 4. The assembly of claim 1, wherein the hollow core is definedby a surface of the sealing diaphragm and an inside surface of thehollow core.